1. Field of the Invention
The present invention relates to a power receiving device and a power transfer system.
2. Description of the Related Art
Information processing devices capable of communicating without contact with a reader/writer (or an information processing device having a reader/writer function), such as a non-contact integrated circuit (IC) card, a radio frequency identification (RFID) tag and a cellular phone equipped with a non-contact IC chip, have come into widespread use.
A reader/writer and an information processing device such as an IC card or a cellular phone communicate with each other by using a magnetic field at a specific frequency such as 13.56 MHz as a carrier wave. Specifically, a reader/writer and an information processing device communicate in such a way that the reader/writer transmits a carrier wave on which a carrier signal is superimposed, and the information processing device such as an IC card receives the carrier wave with an antenna and returns a response signal to the received carrier signal by load modulation.
Further, an information processing device such as an IC card or a cellular phone is driven by a voltage (induced voltage) which is generated according to a magnetic flux when a magnetic field generated by a reader/writer passes through a communication antenna as a power supply. Thus, a reader/writer can supply electric power wirelessly to an information processing device such as an IC card or a cellular phone by transmitting a carrier wave.
A technique of increasing efficiency of wireless transfer of electric power using a carrier wave by performing impedance conversion has been developed. The technique of increasing reception efficiency of an electric wave by means of impedance conversion is disclosed in “HAM Journal No. 98, 1995.7/8” CQ Publishing Co., Ltd. 1995, p. 47.